Benthic Foraminiferal Assemblages Research Articles

Intertidal zonation of live benthic foraminiferal assemblages from mangrove environments around south-west Penang Island, Peninsular Malaysia

Abstract Studies on benthic foraminifera were conducted in the mangrove forests of Teluk Tempoyak, Pulau Betong and Kuala Sungai Pinang, Penang Island, Peninsular Malaysia to examine species composition and distribution patterns in different intertidal zones. Twenty-eight live benthic foraminiferal species were successfully identified at the study locations, predominantly species with agglutinated tests. Assemblages in Pulau Betong and Teluk Tempoyak were dominated by similar species such as Ammonia aoteana, Elphidium hispidulum, Elphidium neosimplex and Trochammina inflata, while Kuala Sungai Pinang comprises a high number of Trochammina inflata and Arenoparrella mexicana. Three species, Aubignyna perlucida, Elphidium neosimplex and Elphidium sandiegoense, were recorded for the first time in Malaysian mangrove forests. Principal component analysis showed that sediment type and organic matter content were the dominant parameters that explained the variation of environmental gradient. Canonical correspondence analysis of these parameters with benthic foraminiferal species indicated that sand particles influenced distribution of the hyaline tests. Species with agglutinated tests were abundant in sediment with rich organic matter in combination with high silt and clay content. Species with hyaline tests dominated lower intertidal zones, while those with agglutinated tests inhabited the area from the middle to upper intertidal zones. This distribution pattern of benthic foraminiferal species mirrored patterns found at other local and global mangrove locations.

New biostratigraphy and microfacies analysis of Eocene Jahrum Formation (Shahrekord region, High Zagros, West Iran). A carbonate platform within the Neo-Tethys oceanic realm

The Eocene Jahrum Formation in High Zagros was studied in Kuh-e- Soukhteh and North Gahrou sections (southwest of Shahrekord region, Chahar-mahal Bakhtiari Province). This formation, composed of limestone, marl, and dolomitic limestone (dolostone), accumulated on a marine platform within the Neo-Tethys ocean realm. It yields a rich foraminiferal fauna, in which three larger benthic foraminiferal assemblage zones were identified. Two assemblage zones in the North Gahrou section were correlated to the Ypresian and Bartonian, and one assemblage zone is represented in the Kuh-e- Soukhteh section and assigned to the Bartonian. In addition, three other groups of benthic foraminiferal associations have been identified based on test wall type (porcellaneous, agglutinate, hyaline) and paleogeographical significance. A discontinuity marked by a hiatus from Cuisian to Lutetian in the North Gahrou section was most probably due to a concealed fault. According to microscopic textures and distribution of benthic foraminifera and other components (peloids, intraclasts, etc.), a gentle depth gradient from the inner ramp to the proximal outer ramp may be reconstructed.

Biostratigraphy of larger foraminifera from the Middle Eocene Jahrum-Pabdeh formations (Zagros region, SW Iran) and their correlation with the planktonic foraminiferal zones

Eocene larger benthic foraminifera including orthophragmines, nummulitids and alveolinids from the Jahrum and Pabdeh formations in the Zagros region are presented. The studied 20-m-thick stratigraphic interval contains, Asterocyclina Gumbel 1870, Nemkovella Less 1987, Orbitoclypeus Silvestri 1907, Discocyclina Gumbel 1870, Nummulites Lamarck 1801, Assilina d'Orbigny 1826 and Alveolina d'Orbigny 1826. This larger benthic foraminiferal assemblage testifies for the shallow benthic zones (SBZs) 15 to 17, which ranges from the middle Lutetian up to the early Bartonian. Further micropaleontological analysis made on intercalated planktonic-rich levels helps calibrate the larger foraminifera biostratigraphy, demonstrating a correlation with the E11 biozone. This confirms that the chronostratigraphic calibration of the SBZs made by previous authors for the peri-Mediterranean area can, through the middle Lutetian to the early Bartonian, be applicable in the Middle East as well.

Spatial Distribution of Benthic Foraminifera in the Neretva Channel (Croatia Coast): Faunal Response to Environmental Parameters

Benthic foraminiferal assemblages have been studied at 11 sediment surface samples located in the Neretva Channel covering the delta habitat and the adjacent open sea areas. The major objective of the investigation was to explore the main environmental parameters affecting the benthic foraminifera compositional changes. To this end, a statistical approach was applied that integrates micropaleontological data with physical, geochemical and sedimentological parameters (total organic carbon and grain size). Statistical analyses identified four distinct groups (cluster A1, A2, B1, B2) corresponding to different environmental settings. Cluster A1 groups samples under Neretva river influence and is characterized by Aubignyna perlucida, Nonionella turgida, Eggerelloides scaber and Rectuvigerina sp.; species able to live in organic-matter-rich sediments and in a wide range of oxygen content. Cluster A2 includes samples distant from the fluvial outlet and samples along the NW coast partially influenced by the Neretva river plume. In these environmental conditions, Ammonia beccarii, Bulimina marginata, Nonionella turgida and Textularia sp. resulted as the most characteristic taxa. Cluster B1 distinguishes the deepest stations which are in connection with the open Adriatic Sea. Here Asterigerinata mamilla, Buccella granulata, Cibicides group, Reussella spinulosa and Textularia sp. reach their maximum abundance associated with coarse-grained sediments. Cluster B2 groups samples collected in the inner bay of the southernmost sector of the studied area characterized by silt and clay and a negligible influence by river inputs. The benthic microfauna is principally composed of Miliolids, Porosononion granosum and Textularia sp.

Eocene‒oligocene larger foraminifera from Libya and their palaeoecologic context

ABSTRACT The lithological characteristics and the larger benthic foraminiferal assemblages of the Darnah and Al Bayda formations in the Wadi Darnah section on the southern side of Darnah city, Libya are described, and bio- and chronostratigraphic units are determined based on diagnostic larger benthic foraminifera and depositional environments. The Darnah Formation yielded three species of Middle Eocene (Late Lutetian) age: Nummulites discorbinous, Nummulites praelyelli, and Nummulites bullatus. The Shahhat Marl and Algal Limestone members of the Al Bayda Formation yielded three species of Early Oligocene (Rupelian) age: Nummulites budensis, Blondeauina bouillei, and Nephrolepidina sp. cf. sumatraensis. The Nummulites biozone SBZ16 (Late Lutetian) constitutes the Darnah Formation, which ends upwards in an unconformity. The SBZ21 biozone (Rupelian) constitutes the Al Bayda Formation. The micro- and macrofaunal content and the lithological characteristics indicate shallow-platform marine environments for the studied rock units.

Biomonitoring of a Nile Delta Lake using benthic foraminifera

Lake Edku, one of the northern Nile Delta lakes, is a shallow brackish coastal lake subjected to domestic and agricultural effluents via two main drains, El-Khairy and Barsik, in addition to the discharge water of hundreds of fish farms. This study measures the responses of the benthic foraminiferal assemblage to the environmental stressors in Lake Edku. Grain size, organic carbon, and seven potentially toxic elements (Cu, Pb, Zn, Cd, Cr, Ni, and As) were determined in nine short cores (25–35 cm depth). The lake was characterized by vertical increase in mud, organic matter, and concentrations of all metals, particularly in the eastern basin at the vicinity of the drain discharges. This trend coincides with a general decrease in species diversity and increase in deformed specimens. The foraminiferal assemblage was dominated by Ammonia tepida (Cushman), a pollution-tolerant and euryhaline species. This study demonstrates that benthic foraminiferal assemblages provide a reliable pollution proxy in the brackish environments of Nile Delta that can be used in the periodical monitoring of the coastal lakes.

Environmental forcing by submarine canyons: Evidence between two closely situated cold-water coral mounds (Porcupine Bank Canyon and Western Porcupine Bank, NE Atlantic)

Within the Porcupine Bank Canyon (NE Atlantic), cold-water coral (CWC) mounds are mostly found clustered along the canyon lip, with individual disconnected mounds occurring nearby on the western Porcupine Bank. Remotely operated vehicle-mounted vibrocoring was utilized to acquire cores from both of these sites. This study is the first to employ this novel method when aiming to precisely sample two closely situated areas. Radiometric ages constrain the records from the early to mid-Holocene (9.1 to 5.6 ka BP). The cores were then subjected to 3D segmented computer tomography to capture mound formation stages. The cores were then further examined using stable isotopes and benthic foraminiferal assemblages, to constrain the paleoenvironmental variation that influenced CWC mound formation of each site. In total, mound aggradation rate in the Porcupine Bank Canyon and western Porcupine Bank was comparable to other Holocene CWC mounds situated off western Ireland. Results derived from multiproxy analysis, show that regional climatic shifts define the environmental conditions that allow positive coral mound formation. In addition, the aggradation rate of coral mounds is higher adjacent to the Porcupine Bank Canyon than on the western Porcupine Bank. Benthic foraminifera assemblages and planktic foraminiferal δ13C reveal that higher quality organic matter is more readily available closer to the canyon lip. As such, we hypothesize that coral mound formation in the region is likely controlled by an interplay between enhanced shelf currents and the existence of the Eastern North Atlantic Water-Mediterranean Outflow Water-Transition Zone. The geomorphology of the canyon promotes upwelling of these water masses that are enriched in particles, including food and sediment supply. The higher availability of these particles support the development and succession of ecological hotspots along the canyon lip and adjacent areas of the seafloor. These observations provide a glimpse into the role that submarine canyons play in influencing macro and micro benthic fauna distributions and highlights the importance of their conservation.

Shelf Ecosystems Along the U.S. Atlantic Coastal Plain Prior to and During the Paleocene‐Eocene Thermal Maximum: Insights Into the Stratigraphic Architecture

AbstractThe Paleocene‐Eocene Thermal Maximum (PETM) is the most pronounced global warming event of the early Paleogene related to atmospheric CO2 increases. It is characterized by negative δ18O and δ13C excursions recorded in sedimentary archives and a transient disruption of the marine biosphere. Sites from the U.S. Atlantic Coastal Plain show an additional small, but distinct δ13C excursion below the onset of the PETM, coined the “pre‐onset excursion” (POE), mimicking the PETM‐forced environmental perturbations. This study focuses on the South Dover Bridge core in Maryland, where the Paleocene‐Eocene transition is stratigraphically constrained by calcareous nannoplankton and stable isotope data, and in which the POE is well‐expressed. The site was situated in a middle neritic marine shelf setting near a major outflow of the paleo‐Potomac River system. We generated high‐resolution benthic foraminiferal assemblage, stable isotope, trace‐metal, grain‐size and clay mineralogy data. The resulting stratigraphic subdivision of this Paleocene‐Eocene transition is placed within a depth transect across the paleoshelf, highlighting that the PETM sequence is relatively expanded. The geochemical records provide detailed insights into the paleoenvironment, developing from a well‐oxygenated water column in latest Paleocene to a PETM‐ecosystem under severe biotic stress‐conditions, with shifts in food supply and temperature, and under dysoxic bottom waters in a more river‐dominated setting. Environmental changes started in the latest Paleocene and culminated atthe onset of the PETM, hinting to an intensifying trigger rather than to an instantaneous event at the Paleocene‐Eocene boundary toppling the global system.

Magnetofossils and Benthic Foraminifera Record Changes in Food Supply and Deoxygenation of the Coastal Marine Seafloor During the Paleocene‐Eocene Thermal Maximum

AbstractContinental shelf sediments along the northeast continental margin of North America contain a magnetofossil‐rich interval deposited during the Paleocene‐Eocene Thermal Maximum (PETM), an abrupt global warming event that occurred ∼56 Ma. These magnetofossils were produced by magnetotactic bacteria and unidentified, iron‐biomineralizing organisms. Previous work shows three distinct magnetofossil endmembers identified from principal component analysis of first‐order reversal curves (FORC‐PCA). The relative proportions of these magnetofossil endmembers varied over time during the PETM. Benthic foraminiferal species associations from the same sediments also vary during the PETM. Here, we compare the variability in magnetofossils and benthic foraminifera and statistically test, for the first time, whether they are significantly correlated. We find that changes in the type of magnetofossils present within the sediment correspond to changes in benthic foraminiferal assemblages, thus reflecting syndepositional conditions such as changes in oxygen, nutrients, and organic carbon concentrations, rather than diagenetic processes. We also find that magnetofossil‐producing organisms may respond to specific environmental pressures differently than benthic foraminifera, and in some cases, may better record these environmental signals. Therefore, FORC‐PCA on magnetofossil‐rich sediments can be used to understand discrete changes in ocean and/or early sediment chemistry over episodes of climate change. These environmental responses are inferred from non‐destructive, reproducible magnetic measurements, adding an independent environmental proxy to more commonly studied microfossil and geochemical proxies. Notably, these measurements only require small bulk sediment samples and do not need to contain calcium carbonate, making this approach ideal where sample material is limited and the record is affected by ocean acidification.

Morphotype analysis and paleoecological implications of Maastrichtian - Paleogene benthic foraminifera from RCCG BH4 Borehole, Eastern Dahomey (Benin) Basin

The Maastrichtian-Eocene paleoecological conditions of eastern Dahomey (Benin) Basin were investigated using benthic foraminiferal morphotypes from the RCCG BH-4 borehole located on kilometer 46, Lagos-Ibadan Expressway, southwest Nigeria. Many previous studies on the basin and other Nigerian sedimentary basins centered on paleobathymetric studies using depth indicator benthic foraminiferal assemblages and planktic/benthic ratio. This present study attempts to categorize benthic species into morphological categories (morphotypes) based on general outline and shape, chamber arrangement, and mode of coiling, and use the distribution of the morphotypes to determine certain paleoecological conditions such as organic matter content, sediment pore water oxygen availability and sediment depositional setting. 25 ditch cutting samples subjected to the kerosene method of micropaleontological sample processing yielded few Maastrichtian – Eocene planktic species (Planoheterohelix globulosa, Morozovella acuta, Parasubbotina pseudobulloides, and Subbotina velascoensis) and fairly abundant and diverse benthic foraminiferal assemblages which we categorized into nine (9) morphotypes designated B2, B3, C1, F, H, I, J, N and Q. Six (6) of these morphotypes (B2, B3, I, J, N, and Q) are adapted to the epifaunal mode of life, while morphotypes C1, F, and H belong to the infaunal types. The dominance of the epifaunal morphotypes within the limestone Ewekoro Formation, and the underlying shaly sand unit of the Araromi Formation revealed a shallow marine (inner – middle neritic), low organic matter content, and oxygen-rich environment of deposition for these units. The infaunal morphotypes show sparse occurrence within the borehole except within the organic intercalation within the limestone unit in which 8 counts of Afrobolivina afra were recorded. The disappearance of species (faunal turnover) within the overlying shale unit (Akinbo Formation) is believed to be a response to heightened organic matter flux, reduced oxygen availability, and other climatic perturbations characteristic of the Paleocene-Eocene boundary. Eponides pseudoelevatus (morphotype N) is believed to be an opportunistic species based on the species’ continued occurrence and increased abundance within the shale unit (Akinbo Formation). The species may have recolonized the environment following improved environmental conditions that ensued after the cessation of the end Paleocene climatic perturbation.

Deglacial to Mid Holocene environmental conditions on the northeastern Greenland shelf, western Fram Strait

The western Fram Strait is the only deep-water gateway connecting the Arctic Ocean and North Atlantic. Consequently, today, the western Fram Strait and the Northeast Greenland shelf receive cold, low saline Polar and Arctic Atlantic waters from the Arctic Ocean incorporated in the East Greenland Current, together with warmer, saline recirculated Atlantic Water masses derived from the West Spitsbergen Current. We present a multiproxy study (grain size distribution, XRF core scans, and benthic foraminiferal assemblages) based on the lower part of the radiocarbon dated marine sediment core DA17-NG-ST03-039G, covering the period from 13.3 to 3.9 cal ka BP. We reconstruct the deglacial conditions of the Northeast Greenland shelf together with Early to Mid Holocene fluctuations in subsurface Atlantic Water and Polar Water advection. The results show that the outer Northeast Greenland shelf was deglaciated and marine conditions were established prior to c. 13.3 cal ka BP. At this time, our data show Atlantic Water masses flowing beneath an extensive sea-ice cover in a glaciomarine setting, potentially related to the Bølling-Allerød warm period. Around 12.9 cal ka BP, the onset of high surface and bottom water productivity may be associated with the Younger Dryas onset. This was followed by a transition towards warmer bottom and subsurface water conditions from c. 11.7 until 10.2 cal ka BP caused by enhanced advection of Atlantic-derived water masses. A cold period with marginal ice zone conditions and enhanced East Greenland Current incursion is evident from 10.2 to 9.4 cal ka BP, succeeded by harsher sea-ice conditions and Atlantic Water inflow, prevailing until c. 7.5 cal ka BP. Holocene Thermal Maximum conditions, characterized by high surface and subsurface water productivity, were promoted by enhanced Atlantic Water flow to the shelf from c. 7.5 to 6.7 cal ka BP. In contrast, the transition towards a cold period with increased drift-ice transport via a strong East Greenland Current is recorded from c. 6.2 cal ka BP and to the end of our record at 3.9 cal ka BP; it was associated with the onset of the Neoglaciation.

Changes in productivity and intermediate circulation in the northern Indian Ocean since the last deglaciation: new insights from benthic foraminiferal Cd ∕ Ca records and benthic assemblage analyses

Abstract. We have measured Cd/Ca ratios of several benthic foraminiferal species and studied benthic foraminiferal assemblages on two cores from the northern Indian Ocean (Arabian Sea and northern Bay of Bengal, BoB), in order to reconstruct variations in intermediate-water circulation and paleo-nutrient content since the last deglaciation. Intermediate water Cdw records estimated from the benthic Cd/Ca reflect past changes in surface productivity and/or intermediate–bottom-water ventilation. The benthic foraminiferal assemblages are consistent with the geochemical data. These results suggest that during the last deglaciation, Cdw variability was primarily driven by changes in intermediate-water properties, indicating an enhanced ventilation of intermediate–bottom water masses during both Heinrich Stadial 1 and the Younger Dryas (HS1 and YD, respectively). During the Holocene, however, surface primary productivity appears to have influenced Cdw more than intermediate water mass properties. This is evident during the early Holocene (from 10 to 6 cal ka) when benthic foraminiferal assemblages indicate that surface primary productivity was low, resulting in low intermediate-water Cdw at both sites. Then, from ∼ 5.2 to 2.4 cal ka, surface productivity increased markedly, causing a significant increase in the intermediate-water Cdw in the southeastern Arabian Sea and the northeastern BoB. The comparison of intermediate-water Cdw records with previous reconstructions of past Indian monsoon evolution during the Holocene suggests a direct control of intermediate-water Cdw by monsoon-induced changes in upper-water stratification and surface primary productivity.

Ecological and Environmental Stability in Offshore Southern California Marine Basins Through the Holocene

AbstractIn the face of ongoing marine deoxygenation, understanding timescales and drivers of past oxygenation change is of critical importance. Marine sediment cores from tiered silled basins provide a natural laboratory to constrain timing and implications of oxygenation changes across multiple depths. Here, we reconstruct oxygenation and environmental change over time using benthic foraminiferal assemblages from sediment cores from three basins across the Southern California Borderlands: Tanner Basin (EW9504‐09PC, 1,194 m water depth), San Nicolas Basin (EW9504‐08PC, 1,442 m), and San Clemente Basin (EW9504‐05PC,1,818 m). We utilize indicator taxa, community ecology, and an oxygenation transfer function to reconstruct past oxygenation, and we directly compare reconstructed dissolved oxygen to modern measured dissolved oxygen. We generate new, higher resolution carbon and oxygen isotope records from planktic (Globigerina bulloides) and benthic foraminifera (Cibicides mckannai) from Tanner Basin. Geochemical and assemblage data indicate limited ecological and environmental change through time in each basin across the intervals studied. Early to mid‐Holocene (11.0–4.7 ka) oxygenation below 1,400 m (San Clemente and San Nicolas) was relatively stable and reduced relative to modern. San Nicolas Basin experienced a multi‐centennial oxygenation episode from 4.7 to 4.3 ka and oxygenation increased in Tanner Basin gradually from 1.7 to 0.8 ka. Yet across all three depths and time intervals studied, dissolved oxygen is consistently within a range of intermediate hypoxia (0.5–1.5 ml L−1 [O2]). Variance in reconstructed dissolved oxygen was similar to decadal variance in modern dissolved oxygen and reduced relative to Holocene‐scale changes in shallower basins.

Long-chain alkenones in the Shimosa Group reveal palaeotemperatures of the Pleistocene interglacial Palaeo-Tokyo Bays

The Shimosa Group, a Middle- to Late-Pleistocene sedimentary succession, has been the focus of stratigraphic attention because it lies beneath the Tokyo metropolitan area of central Japan. It is also of palaeoclimatic significance because it contains important interglacial marine strata of the past 450,000 years. Because the marine strata of the Shimosa Group were formed in the shallow inner bay known as the Palaeo-Tokyo Bay, rare occurrences of planktonic foraminifera make it difficult to quantitatively reconstruct the palaeo-sea surface temperatures (SSTs). Here, we extracted long-chain alkenones (LCAs) from the core GS-UR-1 penetrating the Shimosa Group to Marine Isotope Stage (MIS) 11. We found that the alkenone unsaturation ratio appears to reflect the SST of the Palaeo-Tokyo Bay formed during the peaks of MISs 5e, 7e, 9, and 11, which was consistent with the inflowing water mass changes inferred from the benthic foraminiferal assemblages. The palaeo-SSTs during each interglacial period were 2–3 °C higher than the pre-industrial levels of Tokyo Bay and seemed to reach a level similar to that of the Holocene thermal maximum. The findings of this study demonstrate that the LCA-based proxy, which has not before been utilised in studies on the Shimosa Group, has strong potential to provide palaeoceanic and stratigraphic information.

Santonian deep sea benthic foraminifera from IODP Site U1513, Mentelle Basin (SW Australia): Reactions of benthic foraminiferal assemblages to surface water cooling at southern high latitudes

International Ocean Discovery Program (IODP) Expedition 369 recovered a stratigraphically complete, Santonian-aged, pelagic sedimentary sequence at Site U1513 on the Naturaliste Plateau (33°47.6084′S, 112°29.1338′E) at ~2800 m water depth. The site was located at ~60°S paleolatitude in Cretaceous times. A total of 59 samples studied from Holes 1513A and 1513B yielded 140 calcareous and nine agglutinated benthic foraminiferal taxa. Gavelinellids (Notoplanulina, Gavelinella, Anomalinoides) and Gyroidinoides spp., are the most abundant taxa overall and also dominate most samples. We also report 382 foraminiferal stable isotopic measurements and infer cooling [of ~5 °C in surface waters and 2 °C at the seafloor] based on changes in δ18O values for benthic and planktonic taxa through the Santonian at Site U1513. Inferred cooling was accompanied by changes in planktonic and benthic foraminiferal assemblages. At Site U1513, benthic foraminiferal taxonomic richness declines by 15 species (from 20– 25 to 5–10 taxa) towards the upper Santonian. Within this interval, epifaunal, oxic foraminifera diminish in absolute and relative abundance, and there is a parallel relative increase in opportunistic taxa and infaunal foraminifera. Changes in benthic foraminiferal communities indicate a shift from oligotrophic to eutrophic conditions in the bottom water despite the general cooling trend. This paper explores the causes and effects of the paleoenvironmental changes in the bottom waters.

Latest Cretaceous and Paleocene biostratigraphy and paleogeography of northern Zealandia, IODP Site U1509, New Caledonia Trough, southwest Pacific

ABSTRACT IODP Site U1509 (Expedition 371), New Caledonia Trough, provides a rare latest Cretaceous–Paleocene record from offshore northern Zealandia. We present new palynomorph and benthic foraminiferal assemblage data that show a transition from a latest Cretaceous vegetated sediment source region to a fully oceanic environment in the Paleocene. Latest Cretaceous (c. 68–66 Ma) non-calcareous claystone was deposited in upper bathyal paleodepths, with abundant plant microfossils that were likely transported in a northwest direction through the Aotea Basin region. A 2–3 Myr unconformity is identified at the Cretaceous/Paleogene boundary. Middle early–late Paleocene (c. 63.5–56 Ma) calcareous claystone shows evidence of deepening, deposited in middle bathyal or deeper paleodepths, and terrestrial input is minor. This latest Cretaceous to Paleocene deepening trend is consistent with inferred evolution of the Aotea and Northland basins further to the east, and other sparse northern Zealandia records, which show a common pattern of post-rift transgression consistent with long-term subsidence. Site U1509 allows for biogeographic extension and modification of the New Zealand Paleocene dinoflagellate zonation, description of a new dinoflagellate and pollen species, better inference of regional paleogeography, and may provide insights into the onset of western Pacific subduction initiation.

Intermediate ocean circulation and cryosphere dynamics in the northeast Atlantic during Heinrich Stadials: benthic foraminiferal assemblage response

AbstractThe interaction between ocean circulation and ice‐sheet dynamics plays a key role in the Quaternary climate. Compared with the surface and deep regions of the Atlantic Meridional Overturning Circulation (AMOC), the study of intermediate depths during key time periods, such as Heinrich Stadials (HSs), remains poorly documented, especially for the northeast Atlantic. Here we use benthic foraminiferal assemblage data to trace palaeoenvironmental changes from ~32 to 14 ka cal bp at ~1000 m depth in the Bay of Biscay. Our results highlight the high sensitivity of foraminifera, with species‐specific responses, to continental (European Ice Sheet dynamics) and marine (AMOC) forcing factors during the last three HSs. In general, HSs were characterised by the concomitant presence of meso‐oligotrophic and anoxia indicator species and the low abundance of high‐energy indicator species. This confirms an overall sluggish intermediate circulation during the three HSs in the northeast Atlantic. HS1 is distinctive for its abundance of high‐organic flux indicator species during its early phase. This is consistent with the fact that HS1 was by far the most important period of ice‐sheet retreat and meltwater release into the ocean over the studied time interval. Finally, foraminifera depict the mid‐HS2 reventilation event due to regional glacier instabilities.

Improved Planktonic, Benthic Foraminiferal and Nannofossil Biostratigraphy Aids the Interpretation of the Evolution at Hole U1468A: IODP Expedition 359, the Maldives

Extended shallow carbonate platform, pelagic, and drift deposits were drilled during International Ocean Discovery Program (IODP) Expedition 359 in the Inner Sea of the Maldives. These sediments yield rich and well-diversified benthic, planktonic foraminiferal and nannofossil assemblages spanning from the early Oligocene to the Recent. We present here the shore-based revised integrated biostratigraphy of these microfossil groups at IODP Hole 359-U1468A together with the paleobathymetric reconstruction. Our data suggests the presence of a late Oligocene carbonate platform, marked by the shallowest water depths of the entire sequence of around 80 m. This carbonate platform sequence occurred from around 29 Ma, the extrapolated minimum age estimate, at least up to 27.5 Ma and possibly up to 25.4 Ma. Up the sequence, similar carbonate production conditions occurred until 22.5 Ma across the Oligocene–Miocene transition, equated at 23.04 Ma, with increased water depths >120 m. Notably, in the time interval approximately from 24 to 21.5 Ma, orbitally induced sapropel layers indicate a change of open to restricted circulation. However, at around 22.5 Ma, pelagic deposition at a distal slope occurred with sedimentation rates of 3 cm/years. This initially occurred in water depths of >350 m but gradually reached deposition in water depths of >500 m, which persisted from 21.12 Ma until approximately the extrapolated age of 12.8 Ma. Sedimentation rates gradually increased to 10.5 cm/1000 years at around 450 m below sea floor, marking the initiation of the drift sequence as identified in seismic lines with an age estimate of 12.8 Ma. The initiation of the drift sequence is also marked by a drastic decrease in the preservation of benthic and planktonic foraminifera from good to very poor at around 12.8 Ma. The drift sequence essentially continued to the present day but was interrupted by two events: the deposition of distinct shallow water benthic shoals and a large hiatus. From 12.8 Ma, a shallowing upward bathymetry is suggested by the occurrence of shallow benthic foraminiferal assemblages that close to around 11.93 Ma reached a maximum water depth of 80 m. This shoal then prograded into the basin and persisted at least until 9.89 Ma. Basin conditions with water depths exceeding 500 m were re-established in the upper part of the sedimentary succession after a hiatus spanning approximately from 9.83 Ma to 2.39 Ma, implying that renewed open ocean conditions occurred in the Pliocene–Pleistocene part of the sedimentary record.

Epiphytic foraminifers as indicators of heavy-metal pollution in Posidonia oceanica seagrass meadows

Because of their toxicity, persistence and difficult biodegradability heavy metals are one of the most significant pollutants in marine environments, including seagrass meadows. Epiphytic foraminifers are conspicuous in the Posidonia oceanica meadows and can be utilized as cost-effective bioindicators. To evaluate the ecological conditions of P. oceanica meadows around the Balearic Islands four indices based on benthic foraminiferal assemblages, such as, the modified FORAM Index (FI’), the “Long vs Short life span” index (ILS), the Foram Stress Index (FSI), and Shannon-Weaver index (H’), were calculated. High index values for all sampling sites with different anthropogenic activities indicated a good ecological status of the seagrass. In contrast, the proportion of abnormal foraminiferal tests (FAI), based on morphological analysis, was variable among the study sites and reach very high abundances in areas with a priori low anthropogenic impact. Although there is not a univocal cause-effect pattern between the occurrence of deformed individuals and heavy metal pollution (such as Cu, Zn, Cd, Pb, Co, Ni, As and Sn), abnormal growth forms were significantly more abundant in sites where the tests contained higher concentrations of trace elements, and certain deformities (occurrence of protuberances and supernumerary chambers) seemed to be associated with specific pollutants (Zn, Ni and As). The disparity between the foraminiferal biotic indices and the percentage of aberrant forms associated with the heavy metal uptake can be explained by differences in the type of environmental impact and the mineral composition of the foraminiferal tests. Thus, the use of foraminifera as bioindicators, combining different approaches such as ecological indices, quantification of abnormal growth patterns and geochemical analysis of their tests, are very helpful in determining the health of seagrass meadows ecosystems. The indices are proxies to show dominant conditions over a large area, whereas the morphological and geochemical analysis of the foraminiferal tests shows very localized but long-lasting impacts with sublethal effects.

Groundwater Salinity and Particulate Organic Carbon Flux Control Benthic Habitats in Anchialine Environments on Millennial Timescales

The environmental conditions and habitats in Bermudian underwater caves have responded to vertical aquifer migration and groundwater salinity changes associated with sea-level rise since the last glacial maximum. Recently, a large database of modern benthic foraminifera in Bermudian caves were found to be highly sensitive to both the amount and source of particle organic carbon (POC) transported to the sediment-water interface, consistent with similar timewise analysis of foraminifera in a Mexican flooded cave. Here we provide evidence that while benthic meiofaunal communities in Bermuda’s underwater caves are primarily controlled by groundwater salinity changes on millennial timescales from sea-level change, they are secondarily controlled by the POC source and supply deposited in the cave through time. Benthic foraminiferal assemblages were evaluated in the best-preserved stratigraphic succession currently known from an underwater cave. In the case of Palm Cave, POC flux changes were driven by changes in seawater-groundwater circulation dynamics caused by flooding on the carbonate banktop, and the inherited geometry of the cave system itself. These results demonstrate that benthic meiofaunal communities in anchialine environments are highly sensitive to changes in the source and quantity of POC through time. This work also enables a better understanding of the environmental conditions associated with preserved meiofaunal remains in global cave sediment. These results indicate that if the POC flux to the subsurface increases from coastal urbanization on karst landscapes, subsurface anchialine communities are likely to respond.